Currently, the Department of Defense maintains a large inventory of documentation for electronic systems. Usually, this existing documentation is in the form of schematic drawings of electronic circuitry either in hard copy (paper or other similar media) or in a scanned image file. The term schematic drawing shall refer to a drawing that shows by means of graphic symbols, the electrical connections and functions of a specific circuit arrangement. In order to respecify or remanufacture these electronic circuits, as a part, board or system, a considerable amount of time and human effort is required to collect and understand the circuit information from the circuit drawing. Most of this time today is spent recreating the schematic drawing into a computer-aided design (CAD) software program or into a circuit description language. The ability to respecify and remanufacture electronic circuits is essential to the Department of Defense's and industry's ability to maintain and upgrade system electronics.
CAD programs put the information from the drawing into netlist formats. A netlist is a representation of a circuit in a form which lists a series of nets and shows the ports of which circuit are connected to each net. A net is a single electrical path in a circuit having the same signal value at all points wherein a single net can connect to multiple components. CAD programs use either a standard or a proprietary format to store netlist information about a circuit in a form that is generally easy to transfer to other CAD programs and is linked to situational models, which allow direct links between the design, modeling, simulation, and manufacturing phases of the circuit design.
In addition to the proprietary formats (generally used with a single software developer's CAD program), there are a number of standard formats for information exchange within and between different CAD developers. Though the details of these formats may differ, the basic information is the same: components and interconnections between the components. The VHDL is an industry and Department of Defense standard for the documentation, design and simulation of digital electronic circuitry. VHDL is a human and computer readable format used to import design information directly into CAD programs. (The other different types of circuit description languages exist, such as Verilog Hardware Description Language and the Electronic Design Interchange Format (EDIF), are similar to VHDL in concept, and are used for design transfer, but differ in other details which are not pertinent to this disclosure.) Most commercial CAD programs provide a fully automated and integrated manufacturing path from VHDL documentation to integrated circuit fabrication. Since VHDL provides manufacturing technology independent documentation of a digital integrated circuit, it is ideal for the purpose of documenting Department of Defense and industry digital electronic systems for system upgrades and full life cycle support.
Although scanned images of schematic drawings have been generally used in computerized document management systems, these scanned images have not been effectively used in CAD or electronic circuit description languages because these images lack the necessary format information concerning the components and interconnections that are required by these programs/languages. Although research has been conducted in recognizing scanned electronic circuit drawings, these efforts have primarily focused on symbol recognition and character extraction. See for example "Circuit Comparison by Hierarchical Pattern Matching," by Pelz et al, Proceedings of 1991 Conference on Computer-Aided Design, November 1991, Pp 290-293; "A New Input Method for CAD-Automatic Read In Technique Of Paper Drawings," by Shi et al, Proceedings of 1991 International Conference on Circuits and Systems, June 1991, pp 431-433; "Representation, Classification and Modelling of Graphs for Efficient Pattern Recognition in Line Images," by Maderlecher et al, Proceedings of the 9.sup.th International Conference on Pattern Recognition, November 1988, vol. 2, pp. 678-680; and "A Knowledge-Based Graphic Description Tool for Understanding Engineering Drawings," by Yu et al, Proceedings of the 1.sup.st International Conference on Systems Integration, April 1990, pp. 302-309. However, to date, there has been no publications or references to devices that extract circuit interconnections based on a full schematic understanding or a generation of a complete netlist representation from a scanned image. Accordingly, there is a need in this art to provide a complete bridge between scanned images of schematic drawings and the functional CAD or description language formats of the schematic drawings.
The present invention addresses such a need.